code: def check_nested_foreach(graph):
      msg = (
          "Nested foreaches are not allowed: Step *{0.name}* is a foreach "
          "split that is nested under another foreach split."
      )
      for node in graph:
          if node.type == "foreach":
              if any(
                  graph[p].type == "foreach" for p in node.split_parents
              ):
                  raise LintWarn(msg.format(node))
  
imports: import re
  from .exception import MetaflowException
  from .util import all_equal
label_desc: Use image node_id 15 for calling a global function with example usage: check_nested_foreach(graph) without return types